The abnormalities in the functioning of the thyroid gland are common in a pregnant woman and it is associated with the labor or delivery complications such as a preterm or a premature birth, a miscarriage and the adverse health outcomes (such as a hypoglycemia in both the newborn child and the mother).

Between two and ten percent of the pregnancies in the United States are linked to the development of gestational diabetes (a common metabolic pregnancy complication) due to the high thyroid hormone levels.

A longitudinal study on the early pregnancy suggests a direct association between the risk of gestational diabetes and the free triiodothyronine (fT3) levels and the ratio between the free triiodothyronine (fT3) and the free thyroxine (fT4 or FTI). The study also shows these risks are independent of other risk factors of gestational diabetes.

The researchers have conducted a study on 107 women with gestational diabetes and 214 women without gestational diabetes, aged between 18 and 40 years. They used the Fetal Growth Studies-Singleton cohort data for the study purpose. The researchers have conducted a separate analytical study during the first and second trimester to find out the risk of gestational diabetes. They measured the following markers of the thyroid in the four pregnancy visits during the first and second trimester.

The researchers have calculated the fT3:fT4 ratio and determined the status of gestational diabetes from the medical record of the participant. The researchers accounted for risk factors such as the status of the thyroid autoimmunity (linked to genetic background and gender. TAI) and major risk factors for gestational diabetes such as ethnicity, age, and body mass index(BMI) before the pregnancy in the study.

The study also shows a direct association between fT3 and the diagnosis of gestational diabetes during the first and second trimester. But there was no relationship between the free thyroxine (fT4) and thyroid-stimulating hormone (TSH) and the risk of gestational diabetes.

Researchers think that the increased conversion of free thyroxine (fT4) to T3 may increase the free triiodothyronine (fT3) levels and cause gestational diabetes in a pregnant woman.

This was the first study providing the longitudinal data on the association between the markers used to assess the functioning of the thyroid (and fT3:fT4 ratio) and the risk of gestational diabetes. Researchers have suggested that the screening for thyroid disease during the early to middle of the pregnancy to prevent the adverse pregnancy outcomes. There are plans to conduct an analytical study on the effects of these hormones in fetal growth and outcomes. There is a need to conduct another study before coming to the clinical practice guidelines and the recommendations.

This study was supported by the Eunice Kennedy Shriver National Institute of Child Health and the Human Development (NICHD) and the American Recovery and Reinvestment Act of 2009 (ARRA, sometimes called the "Recovery Act").

Senior author of the study was Dr. Cuilin Zhang, MD, MPH, Ph.D., Senior Investigator, the National Institutes of Health (NIH). The study was published June 7, 2018, in the Journal of Clinical Endocrinology & Metabolism. Title of the article was "A Longitudinal Study of Thyroid Markers Across Pregnancy and the Risk of Gestational Diabetes." DOI: doi.org/10.1210/jc.2017-02442

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